breaker coordination across transformer

[Tfret]

I have an application where I need to coordinate the thermal magnetic settings of two breakers on opposite sides of a 2400 / 460 step down transformer. Do I simply use the transformer ratio to convert the primary side current into resultant secodary side current?

 

[mull982]

Take the kVA rating of the transformer divided by the secondary voltage, which in our case is 480V to get the secondary current in amps.

If you have a three phase transformer then you need to go a step further and divide the result that you got above by a factor of 1.73. Your calculation would look something as follows:

Secondary FLA = kVA rating / .480V / 1.73

 

[ron]

Tfret,
Yes.
You draw the curves at the same "reference voltage"

 

[don_resqcapt19]

Why do you need to corrdinate the primary and secondary breakers? The result is the same no matter which breaker opens.